Thousands of security forces in southern Thailand are on high alert after warnings that Islamic militants may stage major attacks this week - exactly a year since a deadly raid that triggered a spate of violence in the region. Hundreds of people have been killed in almost daily attacks in the region.

An early morning attack on an army base on January 4, 2004, killed four soldiers, and triggered a year of violence in Thailand's Muslim majority provinces that has so far led to the deaths of more than 500 people.

No one claimed responsibility for that first attack. However, the Thai government says it and subsequent attacks have been the work of loosely organized Muslim militants - allegedly led by Muslim teachers, four of whom were arrested last month and will soon go on trial.

The spate of bombings, shootings and arson attacks have targeted teachers, monks, students and policemen in the provinces of Pattani, Narathiwat, Songhkla and Yala. The violence has disrupted the lives of residents and discouraged investment in the impoverished region.

A group called the Pattani United Liberation Organization warned of attacks this week to mark the anniversary of the army base raid.

However, Sunai Phasuk of Amnesty International in Bangkok says it remains unclear who is really behind the violence.

It has been a year already, there's increased militarization, martial law has been imposed, increasing number of police have been deployed into southern Thailand, but until today, they couldn't provide any answer to the Thai public," he said. "This is very disturbing, in a sense that the government cannot identify who are they dealing with."

The region, which borders Malaysia, was annexed by Thailand 100 years ago, and a majority of its residents are Muslims, although Thailand as a whole is overwhelmingly Buddhist.

Separatist groups formed by ethnic Malays were active in the area until the 1970s. Security experts say the current violence may be linked to separatist guerillas or local criminal gangs, or both.

Analysts say general discontent over the region's poverty has come together with extremist Islamic influences to foment the latest unrest.

Thai Prime Minister Thaksin Shinawatra has suggested that some of the militants have trained in Malaysia, and have taken refuge there after carrying out attacks.

The government has responded to the violence by sending more security forces and investment to the region, and has cooperated with Malaysia to stem possible cross-border terrorism.

Prime Minister Thaksin said last month that security was improving. "[The situation is] better and better, but it [militants] might be temporarily fight back a little bit, but I think we are in good control," he said.

But Panitan Wattanyagorn, a security expert at Thailand's Chulalongkorn University, says the government lacks a comprehensive solution to the problem.

He also says that as the government has failed in its attempts to curb the violence, the militants have grown stronger.

"They are now more popular. Their ideologies are now more visible," he said. "They are also able to get connected to various elements overseas and there have been more recruits."

Mr. Sunai, the human rights activist, says incidents such as the deaths of more than 80 Muslim protesters at the hands of the security forces in October have not helped the government's cause.

"The Muslims on the one hand, they understand that the government's trying very much to bring normalcy to southern provinces, but on the other hand, they also see the government appear to be insensitive and overly violent," he said.

The trial of the four suspected Muslim leaders will be the first legal effort to bring justice to the victims of the unrest. The four have been charged with treason, and could face the death penalty.

Mr. Sunai says the trial will be a test case.

"If the government can prove it, then it may be a new chapter in fighting violence in southern Thailand," he said. "But if it falls back to previous categories of summary arrests, false confessions and torture during detention, then it will further deteriorate the situation, the anger and frustration among the Muslims population against the government."

Prime Minister Thaksin said Sunday the government is on track to solve the problem. He says the security forces are chasing dozens of suspected militants, and the campaign will make it harder for the militants to mount further attacks.